Gas engines which are operated by burning gaseous fuels (fuel gases) such as natural gas and city gas are known. Theses gas engines can obtain high efficiency and high output. Therefore, gas engines are widely used mainly for power generation engines for regular and emergency use, engines for construction machines, engines mounted on ships, vehicles, and so on.
Patent Document 1 describes a premixed combustion type auxiliary chamber gas engine. In the gas engine disclosed in Patent Document 1, when a piston approaches a compression top dead center in a main combustion chamber and fuel gas in the main combustion chamber is compressed, the fuel gas supplied into an auxiliary chamber is ignited by a spark of a spark plug provided in the auxiliary chamber. Therefore, a flame is generated from the auxiliary chamber, and this flame is injected from a mouthpiece provided in the auxiliary chamber into the main combustion chamber. Then, a mixed gas in the main combustion chamber is ignited by this flame.
A gas engine generally includes a cylinder block (crankcase) and a cylinder head. The cylinder block has a hole which opens toward the cylinder head and accommodates a piston. A cylindrical cylinder liner which fat us a sliding surface for the piston is installed inside this hole. The cylinder head is fastened to the cylinder block by a bolt or the like and occludes an opening of the cylinder block at that time. A space surrounded by the cylinder head, the cylinder liner and the piston serves as a main combustion chamber to which mixed gas is supplied.
A seal member such as a gasket for sealing the main combustion chamber is provided between the cylinder block and the cylinder head. Generally, the seal member is sandwiched between the cylinder block on an outer circumferential side of the cylinder liner or the cylinder liner and the cylinder head. The seal member is sandwiched between the cylinder head and the cylinder block and pressed by an axial force of the bolt fastening the cylinder head and the cylinder block and exerts high sealing performance.